But in an upcoming interview with Oprah on Oprah's Next Chapter, Letterman actually pays Leno a compliment. Then again, it's of the backhanded variety."I will say, and I'm happy to say, that I think he is the funniest guy I've ever known," Letterman said of Leno. "Just flat out, if you go see him do his nightclub act, just the funniest, the smartest, a wonderful observationist and very appealing as a comic. Therefore, the fact that he is also maybe the most insecure person I have ever known — I could never reconcile that."